Power supplies are traditionally device-specific, in that the output voltage of the power converter, whether it be an AC/DC or DC/DC adapter, must be voltage-matched to the host device it was designed to power.
Devices which use an external (or internal) power converter are often designed to operate both with batteries and/or a power adapter. The adapter may be only a substitute for the internal batteries, for example, tape recorders, personal audio or video equipment, hand-held video game machines, etc. This is often the case when the batteries are non-rechargeable, so that the power supply is providing an alternate means of primary power. This enables the user to elect to operate the powered device some of the time with the power adapter, for example a PDA (Personal Digital Assistant) which normally operates on non-rechargeable pencells when being transported, but which also has an optional power adapter for use when the handheld computer is being used in the office or home.
In this case of a power supply which is acting as a battery surrogate, the power adapter is matched to the voltage of the removable batteries. Since there are so many combinations of cells which can be put together to create a battery pack, as well as slightly different voltages from the various types of battery cell chemistries, the operating voltage of any electronic device can vary significantly within the same type of electronic device, whether made by the same or a different manufacturer.
Consumers have some sense of the power supply incompatibility issues, and many know that you cannot plug a 16 volt power adapter from your laptop into a 7.2-volt cell phone. The manufacturers of such devices reinforce that thinking by intentionally installing a proprietary connector on the power supply, so that their power adapter will only mate with their electronic equipment. This provides some measure of safety, in that it helps prevent an incompatible, voltage-mismatched power supply from damaging electronic equipment.
This dedicated power supply model creates a series of problems. As the manufacturer builds more and more variants of its electronic products, each new voltage-specific power supply generates a new corresponding SKU (the Sales Kit Unit is an inventory number, typically a barcode). For example, Business Week (Nov. 4, 1996) reported that Toshiba, the world's leader in laptop computer sales, had released 15 new models of its mobile computers. Over time, the mere process of inventorying and warehousing a large number of power adapters becomes a labor and time-intensive activity. For a consumer electronics manufacturer who may release a dozen or more new products each year, the problem can become significant enough that a separate division, often known as “spares” or “accessories,” becomes necessary.
The federal government requires that manufacturers make replacement parts, such as power supplies, available for seven years. In other countries, the mandated time during which accessory items like power supplies must be kept in inventory is as long as 20 years. The logistical problems, as well as the huge cost to be compliant, has a significant effect on manufacturers' profitability.
Consumers, being dependent on the manufacturer to sell them a replacement or second power supply, are subject to product unavailability, power supplies which are back ordered, and the general inconvenience and loss of time to get an order processed and shipped.
All power supplies tend to look strikingly similar to each other. This is especially true in mobile computing, where a handful of power converter manufacturers supply virtually all of the laptop manufacturers. To minimize costs, the same plastic housings are used for power supplies which have significantly different voltages, i.e., they all look alike, but are not interchangeable. This can be very frustrating to a corporate MIS (Management Information Systems) manager, who may be responsible for several thousand laptops throughout the company. It is not atypical that the MIS manager is responsible for purchasing, inventorying and distributing significant numbers of diverse-voltage power supplies. Keeping the proper number of the correct power supply, which corresponds to its matched laptop, requires time and effort. Maintaining a sufficient inventory of each brand and model of power adapter leads to high costs. Lost time, i.e., productivity, becomes an issue if the manufacturer does not have a particular power supply in stock.
While, as noted, manufacturers attempt to ensure that their device-specific power supply will only fit the equipment for which it was intended by using a slightly different connector, there are only so many connector designs available. For example, there are several dozen combinations of outer-barrel-diameter, and center-pin-diameter barrel connectors available. Generically known as a “5 mm” barrel connector, it is used extensively as a powerline interface throughout the consumer electronics and mobile computing industries. Once one manufacturer has used all the non-interchangeable combinations, it must find a new connector design, or start reusing the same connector family.
Some manufacturers, in an attempt to find more combinations, switch the polarity of the pin and barrel. The consumer, to whom all of these devices look amazingly alike, can easily find a power supply which looks like the one being replaced, has the correct voltage, and even has the same mechanical connector. Having verified all of the visual information, the consumer may not know that the pin and barrel were configured as reverse polarity for that equipment.
The impact of all of this consumer confusion, and product-mandated complexity by the manufacturers, is expressed in an article titled “Eureka! Laptops That Share Parts,” by Stephen H. Wildstrom. Mr. Wildstrom, in his article in Business Week (Jul. 14, 1997, page 14), states that:                “Often, I'd like to use an accessory—a spare battery or an AC adapter left behind from a previous model. But these old parts never fit new notebooks because the design has changed.        “This is more than an annoyance for lots of laptop buyers. For companies that have invested many thousands of dollars in docking stations and spare disks—or even the individual buyer who popped for a spare battery and connection to a car's electrical system—the inability to reuse components involves real money. Corporations, which often buy top-of-the-line notebooks for senior executives and entry-level machines for sales or service people in the field, want to minimize the cost of stocking a common pool of spare parts.”        
The author then points out why his ideal of totally interchangeable and reusable power-related accessories may be difficult to achieve:                “It can be hard for manufacturers to simplify their customers' lives. The switch from 486 to Pentium processors required major laptop redesigns to deal with increased power and cooling requirements.”        
Power supplies, because of these complex issues, particularly that of multiple SKUs, are not products which lend themselves to the normal distribution and sales channels. Numerous SKUs lead to large inventory, warehousing and display requirements, so the power adapter is a poor candidate for ever being a locally available product sold in retail stores. Most retailers simply ignore power supplies as a marketable product class.
This is very unfortunate, because the power supply is definitely a “must have” accessory. A laptop computer is quickly rendered unusable if no power supply is available. Laptop computers do not operate with replaceable primary batteries. Unlike tape recorders, video game players, audio CD players, etc., which can use either disposable drycells, or rechargeable batteries (with the appropriate charger), mobile computing equipment is specifically designed to be powered from custom, manufacturer-specific rechargeable battery packs. Cellular phones are marketed in the same way. Cellphone battery packs are readily available in retail stores, and via mail order, but laptop battery packs are only obtainable from the manufacturer, or from a small number of mail order companies. Even third-party replacement battery pack companies, such as 1-800-BATTERIES (a mail order battery provider), do not carry power supplies for laptops.
This situation is even more critical if the consumer is traveling, and needs the laptop for productivity. Because operating a laptop on the road elevates the need for ready access to a compatible power converter, in that the manufacturer-supplied power adapter is more subject to damage or loss while traveling, the traveler will lose valuable time and money if there is even a day or two wait to get a replacement from the original manufacturer.
Power adapters found in retail outlets like Radio Shack, and other electronics stores, have been designed and engineered for products such as home and office phones, toys and entertainment devices, etc., which have been manufactured to operate at specific multiple-battery-cell voltages. Their output voltages are specific, normally 3, 6, 9 and 12 VDC. These are the “normal” voltages which result as multiples of standard 1.25-volt NiCad cells, or multiples of alkaline drycells rated at 1.5 volts per cell. Two alkalines in series equals 3 volts, five NiCad cells (or four alkalines) is 6 volts, six alkalines (now rechargeable, to a limited degree) equates to 9 volts, etc.
Even within this product group, the identical-looking adapter can be 3, 6, 9, 12 VAC. Customer confusion is still an issue, and the rigidly-defined fixed outputs may not match the customer's particular device to be powered. These inexpensive devices are not designed for the voltages and power loads of laptops and other high-amperage computing devices. Because these low-cost power adapters are designed for fixed-based applications, such as phones and video games, they also tend to be quite bulky and heavy, so they have limited appeal for the consumer who wants a power supply which is small and lightweight enough to fit into a briefcase for travel.
While the same electronics stores stock power supplies which are labeled “universal,” these adapters are only voltage-selectable. These “universal” adapters conform to the classic 3, 6, 9 and 12-volt outputs, and a four-position switch selects the desired output voltage. While offering flexibility, these devices are far short of any true universally-voltage-compatible power supply.
In the mobile computing industry, one or two companies have tried to resolve the issue of a true “plug 'n play” universal power supply. Nesco Battery Systems, of Van Nuys, Calif. claims a universal” power adapter system. “The SmartAdapter System” requires three modules. The first device is a 115-220 VAC input, +15 VDC @ 2.8 A output module which measures 2.25×1.5×5.5″ and has a short DC-out cord with a tethered female receptacle from a car cigarette lighter connector.
To this AC/DC converter module a second device is attached by a mating male car-adapter plug on a coiled cord. This “SmartSupply,” as Nesco has named this module, specifies a 10-30 VDC @ 30 W input, and delivers 5-30 VDC output, rated at 25 W max. This car-adapter device is stated by Nesco to be a “programmable DC power supply.”
The third device is a short length of cable called the “SmartCord.” This cord has an electronic identifier, which may be some sort of chip in one of the connectors which, according to Nesco's package information, “ . . . sets the specific output parameters of the SmartSupply [sic] and provides the proper power connector.” Thus one “SmartCord” is needed for each laptop, portable printer, or external peripheral, so a different cord is required for every externally-powered device.
“The SmartAdapter System,” as marketed by Nesco, is dependent upon a factory-pre-configured, device-specific chip embedded in the “SmartCord's” connector. As such, this “smart” technology is strikingly similar to that shown in U.S. Pat. No. 5,570,002 to Castleman (29 Oct. 1996). Castleman also relies on a read/write chip in the power supply's output cord to identify each specific powered device. Also, U.S. Pat. No. 5,510,691 to Palatov et. al., (23 Apr. 1996) inserts an entire voltage-specific “micro-brick” into the last of the three cord system. Whether one is embedding a single chip in a cord, or an entire power module full of components, the net result is that both Castleman and Palatov require there to be a selection process by the consumer when purchasing these devices. The only “smart” requirement is that the consumer must be smart enough to read a chart and purchase the right combination of three modules.
The consumer must acquire this hidden key in the Nesco “SmartCord” which matches the specific voltage of the laptop or peripheral device. This is done with a substantial product-identifier chart, which lists hundreds of laptops, and their matched “SmartCord” identifier. With any device which requires such look-up tables, being “universal” is determined by how comprehensive and up-to-date the chart is.
One can also readily see why SKU issues are a concern with power supplies, in general, and specifically why any distributor or retailer would have concerns about purchasing and displaying hundreds of Nesco “SmartCords.” To stock 200 cables, which would not include every available “SmartCord” variant, would total a market value of $4,000.00 (at the retail price of $20.00 per unit). For a merchant to carry any depth of inventory in just the most popular “SmartCords,” it could easily amount to $10,000.00. Add to this a reasonable quantity of “SmartSupplies,” (retail price $64.95) as well as a matching quantity of the third required device, the AC/DC power converter (retail price $49.99), and the real impact on a retailer by stocking Nesco's complex, multiple-SKU “universal” power supply becomes obvious.
The combination of the three Nesco devices (and you must have all three for the product to work in a wall outlet) weighs about 18 ounces. By comparison, a typical laptop power adapter weighs approximately 6-8 ounces. Furthermore, the entire assembly, with its cigarette lighter adapters (male and female) and two modules, coiled cord, etc., makes for a bulky and cumbersome power source, not well suited to traveling.
The Nesco technology does have a wide-input-voltage-range car adapter as part of its elaborate construct, which delivers a slight benefit to the consumer, but the need for a device-specific interface cord for each powered device offsets the car adapter advantage. For a mobile computing traveler, or the worker who prefers to use a laptop in the office or home, the same issues of having to locate and purchase some proprietary hardware perpetuates the various problems described above.
The previously cited example of the MIS manager relates to Nesco directly. Three Nesco modules are required, and the MS manager would need to purchase numerous sets, at a retail value of $135.00 each. In our model of a company which supports 1,000 laptops, the total cost of ownership is $13,500.00, to outfit the entire company. One would have to retrofit every laptop in the company, otherwise the desired effect of total compatibility and interchangeability would be defeated. By comparison, the average price of a replacement power supply from the manufacturer is $80.00, although some high-end notebooks have replacement power adapters that sell for $250.00+.
For an MIS manager, acquiring and inventorying device-specific and virtually identical-looking “SmartCords” can be frustrating, since some sort of non-removable color coded labels might have to be applied to each “SmartCord” and its matching laptop. These Nesco “SmartCords” are only 18″ long, and can readily be lost or misplaced, especially while packing or unpacking for a business trip.
This “SmartCord” strategy is best captured in a humorous article by Douglas Adams, famed for his Hitchhiker's Guide to the Galaxy book series. In the September 1996 issue of Macworld Magazine, Adams wrote an article titled “Dongly Thing: A Pox on the Panoply of Plugs.” He writes:                Time to declare war, I think, on little dongly things. More of them turned up in the post this morning I'd ordered a new optical disc drive from an American mail-order company, and because I live in that strange and remote place called “Foreign,” and also because I travel like a pigeon, I was keen to know, when ordering it, if it had an international power supply.        “Yes, it does,” said Scott, the sales assistant.        “You're sure it has an international power supply?”        “Yes,” repeated Scott “It has an international power supply.”        “Absolutely sure?”        “Yes.”        This morning it arrived. The first thing I noticed was that it didn't have an international power supply. Instead it had a little dongly thing. I have rooms full of little dongly things and don't want any more. Half the little dongly things I've got, I don't even know what gizmo they're for. More importantly, half the gizmos I've got, I don't know where their little dongly thing is. Most annoyingly, an awful lot of the little dongly things, including the one that arrived this morning, are little dongly things that run on 120 volts AC-American voltage, which means I can't use them here in Foreign (state code FN), but I have to keep them in case I ever take the gizmo to which they fit (provided I know which gizmo it is they fit to) to the USA.        What, you may ask, the hell am I talking about? The little dongly things I am concerned with (by no means the only species of little dongly things with which the microelectronics world is infested) are the external power adapters which laptops and palmtops and external drives and cassette recorders and telephone answering machines and powered speakers and other incredibly necessary gizmos need to step down the main AC supply from either 120 volts or 240 volts to 6 volts DC. Or 4.5 volts DC. Or 9 volts DC. Or 12 volts DC. At 500 milliamps. Or 300 milliamps. Or 1200 milliamps. They have positive tips and negative sleeves on their plugs, unless they are the type with negative tips and positive sleeves. By the time you multiply all these different variables together, you end up with a fairly major industry which exists, so far as I can tell, to fill my cupboards with little dongly things, none of which I can ever positively identify without playing gizmo pelmanism. The usual method of finding a little dongly thing that actually matches a gizmo I want to use is to go and buy another one, at a price that can physically drive the air from your body.        Now why is this? Well, there's one possible theory, which is that just as Xerox is really in the business of selling-toner cartridge, Sony is really in the little dongly power-supply business.        
The aviation community has begun actively to promote easy access to electronic equipment power aboard commercial aircraft by seeking a DC power supply that may be permanently installed in passenger aircraft. Delta Airlines fitted an experimental onboard power system in one aircraft in June 1996. This installation featured a 14.7 VDC car adapter receptacle in the passenger seat arm rests (first class and business class only). The system, called “EmPower,” was engineered and installed by Primex Aerospace Company (previously Olin Aerospace) of Redmond, Wash. Delta Airlines has committed, according to its press release of 30 Apr. 1997, to outfitting 70% of its fleet of 767ERs and MD-11s with EmPower ports. American Airlines has also begun to install this same equipment on its AirBus Fleet®). While Delta's aircraft present the passenger with a proprietary “car-like” cigarette lighter receptacle (it's slightly smaller in diameter), American Airlines is installing a “standard”-sized automotive cigarette lighter receptacle. Thus, connector confusion and incompatible plugs already are perpetuating more SKUs and user confusion.
The “EmPower” system is essentially an in-flight version of an automotive cigarette lighter, with this power port in the passenger seat armrest. Primex provides only a power port, and licenses several manufacturers, such as Xtend Micro Products, Inc., in Irvine, Calif., and Universal Sources, Inc., in Congers, N.Y., and Lind Electronics, in Minneapolis, Minn., to provide DC/DC adapters, which deliver the appropriate device-specific voltage to the passenger's laptop computer.
A sidebar titled “Handy Battery Peripherals,” in the July 1997 issue of Laptop Buyer's Guide and Handbook, describes Xtend's “PowerExtender” in-flight adapters:                “More than 200 different versions will be made available since no standards exist for laptop power systems. For example, a Toshiba notebook requires a different voltage than an IBM ThinkPad. In addition, the power port shapes are different. And various laptop models from the same manufacturer often use different voltages and ports to further compound any attempts to establish adapter compatibility.        “Each Xtend adapter will allow the user to switch between the two sizes of power receptacles currently being considered. Because of the sheer number of adapter types that would have to be stored to satisfy the needs of passengers carrying laptops, airlines probably will not furnish the devices for use or rental. While operating their computers onboard, users will also be charging their laptop batteries. Although only Delta, American, United, and Canadian Airlines are permitting onboard computer use, other carriers are currently reviewing their options, with announcements expected later this year.”        
Delta Airlines has already felt the impact of this passenger confusion, when it paid for a replacement laptop when a passenger used the wrong adapter.
The question of what retailer or computer mail order catalogue company, if any, is prepared to stock some 200 versions of Xtend's “PowerExtender,” at an MSRP of $99.00, remains to be seen.
The author of the sidebar may not have been fully aware of the irony of the Toshiba vs. IBM ThinkPad example that was used to indicate laptop power incompatibilities. The Toshiba notebooks are AC powered, while the ThinkPad requires a DC input. Thus, another spin on this ever-more-complex issue of “universal” power sources is that some airline passengers will need to find power inverters, so that they can benefit from the EmPower 15-volt DC power ports.
The EmPower technology is explained in an article titled “Power System to Make Notebook-Friendly Skies,” in the Jun. 2, 1997 issue of PC Week. The article states that 15 VDC will be delivered to a limited number of seats, with power supplied from the aircraft's generator. While Michael Gaton, the author, praises the EmPower system, he does indicate that the first deployment will only be in first class and business class, specifically on international and long-range flights. The downside to passengers is that “ . . . those who want to use the outlets will need to buy a special power adapter for their notebooks.”
Further, the author states:                “A formal standard for the connector type that will work in these outlets has not been ratified by the airline industry standards board, but of the nine airlines that have announced plans to deploy such a system, only American Airlines has proposed using a unique jack. The first airline to announce plans for in-seat power, American suggested using an automobile-type cigarette lighter jack because of its prevalence.        “The proposed connector standard, ARINC-628, will likely be ratified later this year and uses a smaller connector than the one American Airlines has proposed. This connector would fit in the EmPower outlets.”        
As of November 1997, the AEEC (Airlines Electronic Engineering Committee) has yet to determine the “standard” power port configuration, and it is also reviewing the proper voltage.
Douglas Adams might look askance on this news, since it will definitely mean more and more dongles, adapter plugs, connector incompatibilities, etc. The U.S. automotive industry has recently agreed to accept the new European standard for in-vehicle power adapter ports, and this receptacle is also slightly different from that used by EmPower. Thus, the “standard” cigarette lighter power port looks to be heading the way of many connectors, with proprietary variants on various airlines.
Douglas Adams, in the Macworld article previously referenced, was hoping that some day there would be “one DC power adapter” . . . perhaps something akin to the universal power supply herein described. He especially saw the need for this on passenger aircraft:                “I have to own up and say that, much as I love my [Apple] PowerBook, which now does about 97.8 percent of what I used to use the lumbering old desktop dinosaurs for, I've given up trying to use it on planes. Yes, yes, I know that there are all sorts of power-user strategies you can use to extend your battery life-dimming modes, RAM disks, processor resting, and so on-but the point is that I really can't be bothered. I'm perfectly capable of just reading the in-flight magazine if I want to be irritates However, if there were a DC power supply in my armrest, I would actually be able to do some work, or at least fiddle with stuff.”        
Little did Mr. Adams know that his wish was already coming true, nor did he reckon that the fulfillment of that wish would only spawn anything but a universal, one-power-device solution.
While Delta Airlines, according to a report in Business Traveler News (May 5, 1997), was prepared to make the 10 most commonly used power adapters available to passengers for free, the airline has since decided to not provide any power devices, and instead require the passengers to purchase their own units from vendors like Xtend Micro Products.
The shortcomings of this type of system have already been pointed out. The passenger must bring aboard a specific power module-and-cord assembly for each electronic device he/she wishes to use during the flight. It is not unusual for passengers to bring aboard a personal audio system, with earphones, so that they can enjoy their own musical selections. They can also bring a laptop to the aircraft, in order to do work or, for relaxation, use personal video viewers (Sony's DVD player, for example), tape recorders (with headphones), or the Mitsubishi “SatPhone,” which is a portable satellite phone system in the size and weight of a typical laptop. Depending on the type of laptop, they may also need to use one or more external computer devices, for example, an externally powered CD-ROM drive, a tape back-up device, or a second hard drive, or other storage device. Purchasing and transporting all the necessary power modules can be expensive, bulky, heavy and inconvenient.
Because the external devices mentioned, and others of that type, are sold only with an AC/DC power adapter, and currently only DC power is contemplated for aircraft, the passenger needs to locate and purchase a second power-delivery system specific to traveling. While it may be arguable that this second set of power devices can be used for both an airplane and car, rarely would people need to do active laptop work in their car (some exceptions would be people in service and repair companies, sales reps with local territories, etc.). Outside these particular classes of users, no one uses a computing device routinely in a car, so the double benefits which may seem to be apparent here are not well met in the real world of mobile computing, especially if you consider the obverse, where the group of users benefiting from car-enabled laptop power may not fly on an airplane very much, if at all.
Airline passengers still have to carry two power supplies aboard the aircraft. The standard manufacturer's AC/DC converter is typically used by passengers at the airport, if they belong to any of the airlines' VIP “clubs.” In 1995, the San Jose, Calif. airport conducted test trials with cubicles in the terminal waiting areas where laptop users could work prior to boarding their flights. Mitchell International Airport, in Milwaukee, Wis. has had six such cubicles for a number of years, with laptop amenities, fax machines and phones. These virtual offices are currently getting 50 or so passenger-uses per month. The airport is also expanding the business traveler services to include rental conference rooms, with presentation screens and optional food services, as reported by Business Traveler News. Passengers who need to be productive with their mobile computing equipment will be saddled with carrying some sort of EmPower-specific power adapter, in addition to their AC/DC power supply.
Commercial aircraft-standard voltages available in the cabin are either 115 VAC, or 28 VDC. All devices in the environment are designed to work on one of these two input voltages. The EmPower system, perhaps in reaching for the “it works on airplanes and in cars” dual functionality for the company's third-party power adapters, has designed an inherently electrically-inefficient system. EmPower delivers a nominal reference output voltage of 14.7 VDC to each seat. However, there are a number of electronic devices with operating voltages above 14.7 volts. For example, Apple Computer's PowerBooks are designed as a 24-volt system, so there is a substantial boost from 14.7 volts required. Many PC-based notebook computers also operate at voltages above 14.7, and 20-volt equipment is common in the models which offer high-performance video and presentation capabilities.
Boosting voltage leads to power conversion inefficiencies, which results in heat. Because aircraft cabins are sealed air circulation systems, the heat from multiple power sources is undesirable. On high-density-seating aircraft, where there may be as many as three hundred passengers, having a number of heat sources from power converters has a measurable impact. In converting 14.7 VDC to 24 VDC, for example, a temperature rise of 10-15° F. above ambient can be expected from a reasonably efficient power supply. To this must be added the heat-transfer from the EmPower under-seat AC/DC power converters. Anecdotal information indicates that the EmPower ISPS (In-Seat Power Supply) is inefficient, with perhaps 20+% of the power transfer dissipated as heat. This means a potential 20-25° F. rise in temperature. Thus, the potential cumulative rise in ambient cabin temperature is 30-50° F. for every seat using the EmPower system. This issue of heat has caused Boeing to form a Cooling Working Group within the AEEC, to define and recommend solutions to cooling issues on its aircraft caused by computer equipment.
Industry statistics indicate that some 30-40% of airline passengers use laptops, and another 20-30% carry laptops, but don't routinely use them on the aircraft, as indicated from the 1996 Business Traveler Lifestyle Survey sponsored by Official Airline Guides, of Oak Brook, Ill.
Thus, on an EmPower-equipped wide-body aircraft which has seating for 400 passengers, 120 power modules will be running for hours at a time in an enclosed capsule (some 15 hours, for international flights), which will definitely affect the air conditioning system on the plane. Moreover, these 120 personal, passenger-supplied power adapters, and the equivalent 120 EmPower AC/DC converters to drive them, add to the already burdensome thermal loading created by the existing network of in-cabin power converters for in-flight movies, telephony and galley use. In-flight phones, telephony-based faxes and e-mail, Internet access, TV monitors, personal movie viewers (Sony Video Walkmans will be onboard all of Delta Airlines' L1011-500s, and most of their B-767ERs, according to an airline press release of Apr. 30, 1997), and seat-based TVs, personal Nintendo game players (as supplied by Singapore Airlines), movie projectors, cabin lighting, as well as microwaves, coffee brewers, and even a laptop computer for the cabin crew, etc., all contribute to the total rise in cabin temperature.
Some of these sub-systems, for example in-flight entertainment, require numerous power adapters to deliver passenger-convenience technologies like personal video-on-demand. A typical 72-seat first-class and business-class personal video system requires some 78 AC/DC power modules throughout the cabin area. These power modules are in addition to the EmPower laptop-specific power modules, those for the phone system, etc.
Thus, EmPower's current model of an embedded in-flight power conversion system has deficiencies in energy conservation because of the loss in performance by boosting from a lower input voltage imposing a noticeable thermal load on the aircraft's air control system. These thermal issues also relate to the source of the power, which is an engine-driven generator on the aircraft. With power efficiencies as low as 50%, as noted, the generator must do twice the work to provide the proper power load to the entire cabin. This inefficiency also directly impacts the amount of expensive 100-octane aviation fuel which must be burned, i.e., the airlines have to burn carbon-based fuels to provide laptop power. With the EmPower system, each seat has up to 100 Watts of power load available, so the total load schedule for laptop use on an MD-11-class aircraft can be calculated in kilowatts.
Several host-device manufacturers have attempted to resolve problems of bulky, easily misplaced external power adapters by relocating them into the actual laptop. In the laptop computer industry, Toshiba, Sharp and Compaq have embedded the entire AC/DC adapter into some of their laptop computers. This affords minor improvements over the external-supply model, in that the consumer only needs some type of power cord, typically a “tape recorder”-type electrical cord, to get power from the wall outlet into the device. These cords are not universally available, although a well-stocked electronics store, such as Radio Shack, will likely have the required cord.
This “solution” makes laptops thus configured AC-powered devices. While in-office or in-home usage brings convenience to consumers who own these products, these manufacturers' laptops suffer when they need to be transported . . . and mobility is a key feature of laptop computers, of course. On the road, the car cigarette lighter delivers 12 VDC. A power inverter is required to convert the DC power to AC, and inverters are actually larger and heavier than the original AC/DC adapter, so the trade-off in customer convenience doesn't favor the internal power supply concept.
On commercial aircraft, an inverter is even less desirable. Unlike AC/DC power adapters, which are designed to be EMI clean and relatively noise free, no commercially-available inverter complies with DO-160 specs or other aviation-specific emission or radiation requirements. Furthermore, an inverter is potentially dangerous aboard an aircraft, in that the “live” end of an inverter not connected to its host device, but still plugged into the power input port, has hot 110 VAC exposed to an environment where a spilled drink can create a serious short, and possible fire.
Other problems inherent in this approach are that the weight of the internal power supply is always transported, even for short-duration local trips where the internal battery would provide adequate power. Because the heat generated by the power converter is significant, some manufacturers instruct users to leave the laptop's clamshell case top open during use and for battery recharging. Heat from the internal power adapter also shortens the mean time between failure of nearby components within the laptop (especially if the user ignores the warning, and leaves the laptop closed every time the batteries are recharged). As with any integration/packaging solution, the failure of even a minor component in a bundled, self-contained product requires that the entire device be sent in for service. Furthermore, the consumer cannot order a spare power supply, and achieve the resultant fault-tolerant solution that redundant systems would allow.
Since the power supply is both the most vulnerable component in a failure-analysis model (primarily because of heat and the quality of components used in an accessory item that normally is priced to the OEM customer at less than $10.00), plus the fact that the power converter is the most essential item to the operation of the host device, an embedded power supply is not the best expression of properly implemented power technology.
For example, one laptop manufacturer has reported that its technical support team receives sixty phone calls per week related to replacement or repair of that company's external power supplies. Assuming that even a well-designed power adapter could be cost-effectively built to have only 50% of that sixty-per-week failure rate of the external units, there would still be over 1,500 failures per year with the internal-power-supply-equipped equipment.
The power supply also serves as the power source for a battery charger in devices that use rechargeable batteries. Without a power supply, the device will work on battery power for a finite time, after which it is rendered totally useless. If the device is a mobile computer, the loss of access to data can have significant deleterious effects.
In conclusion, perhaps Douglas Adams best sums up all of the above in his Macworld article, previously cited:                “It's hard to imagine that some of the mightiest brains on the planet, fueled [sic] by some of the finest pizza that money can buy, haven't at some point thought, “Wouldn't it be easier if we all just standardized [sic] on one type of DC power supply?” Now, I'm not an electrical engineer, so I may be asking for the impossible. Maybe it is a sine qua non of the way in which a given optical drive or CD Walkman works that it has to draw 600 milliamps rather than 500, or have its negative terminal on the tip rather than the sleeve, and that it will either whine or fry itself if presented with anything faintly different. But I strongly suspect that if you stuck a hardware engineer in a locked room for a couple of days and taunted him with the smell of pepperoni, he could probably think of a way of making whatever gizmo (maybe even the new gizmo Pro, which I've heard such good things about) it is he's designing work to a standard DC low-power supply.”        